When an aircraft operator reports a suspected hard landing, the aircraft and landing gear manufacturers may be required to analyse the occurrence to determine whether or not the landing gear has been overloaded. However, conservatism exists in the analysis process such that components may be considered overloaded when they have not been.
Should the flight crew suspect a hard landing, they declare a possible hard landing occurrence and a visual inspection of the aircraft landing gear is performed by the maintenance crew of the operator. Neither the subjective assessment by the flight crew nor the visual inspections conducted by the maintenance crew can determine whether the landing gear has suffered an overload. Should the aircraft be grounded because of a suspected overload there are severe economic and/or operational implications for the aircraft operator, however, this is preferable to the aircraft being considered serviceable when actually overloaded due to the safety implications. If the operator suspects there may have been an overload then aircraft flight parameter data (such as aircraft lateral and vertical acceleration, ground speed, pitch and roll angle, aircraft mass and centre of gravity position), is downloaded from the Flight Data Recorder (FDR) and reported to the aircraft and landing gear manufacturers who use dynamic models to assess the loads that the landing gear experienced during the occurrence at spin-up, spring-back and maximum vertical reaction. It is only after this analysis that a decision is made as to whether there has been an overload or not.
For example, critical load cases for the main fitting and sliding tube main landing gear components are the spin-up and spring-back drag axle response loads. The magnitude of these loads is highly dependent on the aircraft vertical acceleration and longitudinal ground-to-tyre friction coefficient, p. However, vertical acceleration is often sampled at only 8 Hz on some aircraft whilst the critical part of the landing, relevant to whether an overload occurred or not, takes less than 125 ms. Therefore, it is likely that the peak vertical acceleration on the landing impact could be missed. Additionally, since μ is not a measured parameter, the aircraft and landing gear manufacturers use a worst-case assumption value in their analysis process. For some events this leads to unnecessarily conservative dispositions of landing gear components, as well as the attachment structure. Therefore, there is a motivation for implementing improved monitoring methods and techniques to maximize operational availability and minimize costs, whilst maintaining an acceptable level of safety.